Nicolas Mackel said there had been “strong interest” from the US and other non-EU firms assessing their options since June’s referendum.
Mr. Mackel was speaking a little over a week after investment giant M&G announced it would be opening funds in Luxembourg, whose government styles it as “the only country left that still loves bankers”.
He said: “They need to come up with contingency plans now; perhaps they should have done it before but were possibly numbed, like so many of us were, into thinking Brexit would never happen.
“They are not looking to move their entire European teams from London; they just want to open a small unit in Luxembourg as well.”
Mackel predicted a maximum of about 30,000 staff would leave the UK capital, split largely between Luxembourg, Frankfurt, and Dublin.
“But London is the major global financial center and will remain the major global financial center. You built London over decades, you have the infrastructure, the depth of expertise that is unmatched,” he said.
However, he predicted a longer “second phase” of the Brexit effect on financial services, which would see new financial companies setting up in Europe less likely to choose the UK as their base.
“For access to the EU, London will no longer be a natural choice,” he said.
He predicted British institutions would follow Switzerland’s UBS, Credit Suisse, Julius Baer and Pictet in opening Luxembourg offices with between 300 and 400 staff to gain access to the EU.
Defecto La Défense, the body responsible for the business district in western Paris, this week made a play to lure City workers from London to France.